The present invention relates generally to a manner by which to synchronize a mobile station in a radio communication system. More particularly, the present invention relates to apparatus, and an associated method, by which a synchronization signal generated by apparatus operable pursuant to a first cellular communication standard can be used to synchronize a mobile station operable pursuant to a second cellular communication standard. An embodiment of the present invention is advantageously utilized in the implementation of a so-called 3G (third generation) cellular communication system. The infrastructure of an existing IS-136 cellular communication system can be utilized to synchronize a mobile station which is operable pursuant to a time frame format defined in a GSM cellular communication system.
In recent years, the utilization of wireless communication systems through which to communicate telephonically has achieved wide popularity. Conventional, voice communications as well as data communications can be effectuated telephonically through the use of such wireless communication systems.
In a wireless communication system, the communication channel formed between a sending and a receiving station is a radio channel, formed of a portion of the electromagnetic spectrum. A wire line connection is not required to effectuate the communication of a communication signal between the sending and receiving stations. Thereby, communication by way of a wireless communication system is possible at a location to which formation of a wire line connection would be impractical or impossible.
Cellular communication systems have been implemented using various communication schemes. Cellular communication systems have been developed which utilize, for example, FDMA (frequency-division, multiple-access), TDMA (time-division, multiple-access), CDMA (code-division, multiple-access) techniques, and various combinations of such techniques.
A cellular communication system includes network infrastructure which includes a plurality of spaced-apart base stations, formed of fixed-site radio transceivers. A user communicates with the infrastructure of a cellular communication network through the use of a radio telephone, typically referred to as a mobile station. The mobile station receives downlink signals on a forward link and transmits uplink signals on a reverse link. Thereby, two-way communications are provided between the infrastructure of the cellular communication network and the mobile station.
With continued improvements in communication technologies and the development of improved circuitry by which to implement such technologies, improvements to cellular communication systems have been proposed. Some proposals pertain to a so-called 3G (third generation) cellular communication standard. Such proposals for the 3G standard are intended to provide a cellular standard permitting universal implementation of a cellular system which shall be able to take advantage of the improved communication technologies to provide a system permitting increased capacity levels of communications and which provide increased communication services.
One such proposal is the UWC-136 HS (Universal Wireless Communications Consortium-136 High Speed) system. In this proposal, certain ones of the technologies and standards promulgated in two existing cellular communication systems are integrated together. Namely, the proposed, UWC-136 HS system integrates together components, and operation, of the existing IS-136/136+ communication system and the GSM/GPRS/EDGE (global system for mobile communications/general packet radio service/enhanced data rates for GSM evolution) system.
A problem associated with such integration is due to dissimilarities of the time frame structures defined in the systems. That is to say, the time frame structure of the IS-136/136+ system and the GSM system are dissimilar. Although both systems are TDMA (time-division, multiple-access) systems, the frames defined in the respective systems are of dissimilar lengths. A frame is a group of time slots. Channels defined in a TDMA system are defined, in part, in terms of the time slots during which signal bursts are transmitted. Both of the systems also define superframes to be groups of frames, and hyperframes to be groups of superframes. But, the superframe lengths and hyperframe lengths are defined to be of dissimilar lengths in their respective systems.
IS-136 and GSM standards define different signals to be used by the mobile in synchronization to the system. In GSM the common control channels are used for synchronization. These channels are SCH (synchronization channel), FCCH (frequency correction channel) and (P)BCCH ((Packet) Broadcast Control Channel). These common control channels are sent in a GSM cell on downlink Carrier CO on its time slot 0. To enable synchronization and measurements by the mobile this carrier needs to be sent constantly at constant power by the base station.
And, the signal bandwidths of signals generated in the different systems are of differing bandwidths. In the IS-136 standard, channels are defined to be of 30 kilohertz bandwidths. And, in the GSM standards, channel bandwidths are of 200 kilohertz bandwidths.
When integrating the standards together to form the UWC-136 HS system, it would be beneficial if the IS-136 DCCH signal could be utilized in synchronization of the mobile to the 200 kHz GSM/GPRS/EDGE carrier. Synchronization of the mobile station from IS-136 DCCH to the 200 kHz carrier could be done quicker than by using the GSM synchronization signals. Also, existing plans for the implementation of the UWC-136 HS system allocates only a limited portion of the electromagnetic spectrum within which to define radio channels. Implementation proposals for the United States, for instance, provide only one megahertz of spectrum, thus necessitating a high level of channel reuse, such as on a 1/3 cell reuse pattern. The common control channels set forth in the existing GSM standard when broadcast in a system utilizing a 1/3 cell reuse pattern might result in excessive levels of interference. A 3G system necessitating a reduced level of signaling, relative to that utilized in a conventional GSM system, would be advantageous.
A manner by which to permit synchronization of a mobile station with the synchronization signals defined in the IS-136 system would advantageously permit synchronization to be performed more quickly and also obviate the need for certain of the synchronization signals utilized in a GSM communication system. The common control channels require bandwidth on the GSM carrier. In a low capacity initial deployment of 136HS it would be beneficial if this bandwidth could be used for packet data transfer. This capacity increase may be possible by using information present on the 30 kHz DCCH in synchronization to the GSM/GPRS/EDGE channel.
The UWC-136HS system will have both the EDGE coverage and 136 coverage in the area of the same cell. This means that the IS-136/136+ and GSM/EDGE base station transceivers will be located in the same cell site. From this perspective it does not seem reasonable that a mobile would need to use time to synchronize to a 200 kHz carrier on a cell where it already has synchronized to the 30 kHz carrier. A faster way would be to utilize information on the 30 kHz channel to make synchronization to the 200 kHz carrier faster.
It is in light of this background material related to synchronization between a mobile station and network infrastructure of a cellular communication system that the significant improvements of the present invention have evolved.
The present invention, accordingly, advantageously provides apparatus, and an associated method, by which a synchronization signal generated by apparatus operable pursuant to a first cellular communication standard can be used to synchronize a mobile station operable pursuant to a second cellular communication standard.
In one implementation, synchronization signals are generated corresponding to standards set forth in the IS-136/136+ interim standard promulgated by the EIA/TIA, and the mobile station is constructed to be operable pursuant to the standards set forth in the GSM (global system for mobile communications) cellular communication standard. Another possible implementation is a multi-mode mobile station capable of operating both according to the IS-136 and/or GSM and/or GPRS and/or EDGE communication standards. Operation of an embodiment of the present invention determines a relative time offset between a frame and time slot on the IS-136 DCCH and a frame and time slot on a GSM/GPRS/EDGE network infrastructure. Responsive to determination of the relative time offset, the mobile station can be placed in time synchronization with the signals generated by the GSM/GPRS/EDGE network infrastructure.
Such an implementation can be utilized, for instance, in the proposed, UWC-136 HS (Universal Wireless Consortium-136 High Speed) cellular communication system, a proposed 3G (third generation) cellular communication system. The infrastructure of an existing IS-136 cellular communication system can be utilized in the newly-proposed system in which the signals formed during operation of the infrastructure correspond to a time frame format defined in the IS-136 communication system.
By utilizing the synchronization signals generated upon the 30 kilohertz carriers defined in the IS-136 system, synchronization of a mobile station to GSM signals can be effectuated more quickly than through synchronization of the mobile station using the GSM, FCCH and SCH channels. Also, through use of the signaling utilized in an IS-136 system, lesser levels of co-channel interference are likely to occur, and smaller cluster sizes, such as those formed pursuant to 1/3 cell reuse patterns, are possible.
Additionally, in the aforementioned, proposed UWC-136 HS system, because control channels conventionally utilized in an existing GSM system are obviated, the bandwidth conventionally required to be reserved for signaling can be used for other purposes. Such channels can be reallocated and used, for example, instead to communicate packet data.
An embodiment of the present invention takes advantage of the close relationship between the multi-frame timing of an IS-136 network and that of a GSM/GPRS/EGPRS network. A period of time can be determined in which both the IS-136 and GSM multi-frames are recurrent. And, analogously, also, a period of time can be determined in which an IS-136 hyperframe and a GSM hyperframe are recurrent. Because of this recurrent relationship, timing differences between slots and frames of the two separate systems are calculable. And, responsive to calculation of the timing differences, synchronization of a mobile station constructed pursuant to the standards of a GSM system can be synchronized through the synchronization signals of the infrastructure constructed pursuant to the standards of the IS-136 system. That is to say, a mobile station that is xe2x80x9ccamping onxe2x80x9d the DCCH of an IS-136 base station can use the synchronization signal generated thereon to become synchronized to the GSM/GPRS/EGPRS channels of the same cell. With only a few additions to the BCCH information on the DCCH, a mobile station is able to calculate the timing differences between the slots and frames of the DCCH and the slots and frames of a GSM/GPRS/EDGE carrier and use such data for purposes of channel synchronization. Thereby, the FCCH and SCH control channels of a GSM system can be replaced with information generated on a DCCH defined in the IS-136 system.
During operation of an embodiment of the present invention, advantage is taken of the fact that the GSM hyperframe length is an integral multiple of IS-136 hyperframe length and that the GSM 26-multiframe length equals to the length of three IS-136 frames. These relationships make it easy to calculate the time difference from any given IS-136 frame-time slot to any given GSM frame/time slot. This idea can be used in the context of a mobile station that needs to work according to both the GSM and IS-136 standards. This will be the case in the UWC-136HS system where the base station will incorporate both GSM and IS-136 base stations. To use this idea synchronization of the GSM and IS-136 forward channels is needed on a cell site only (not network wide). Also, the IS-136 DCCH frame number is extended to count over GSM hyperframe. The same idea applies to any two TDMA systems in case the hyperframe of one is an integral multiple of the hyperframe of the other.
In these and other aspects, therefore, the apparatus, and an associated method, is provided for calculating a relative time offset by which to offset a synchronization signal generated in a communication system by network infrastructure which is operable pursuant to a first TDMA (time-division, multiple-access) communication scheme having a first time frame definition defined therein. The mobile station is operable pursuant to a second TDMA communication scheme having a second time frame definition defined therein. A determiner is coupled to receive the synchronization signal and is operable responsive thereto. The determiner determines an order number representative of a first-communication scheme time frame located within a sequence of the first-communication-scheme time frame at a selected determining time. A converter is operable responsive to the order number determined by the determiner. The converter converts the order number to a corresponding frame number of a second-communication-scheme time frame number. A timing offset calculator is operable responsive to a value representative of the second-communication-scheme time frame number formed by the converter. The timing offset calculator calculates a relative time offset between a first time frame of the sequence of the first-communication-scheme time frames in which the first-communication-scheme time frame, the order number of which the determiner determines, is located, and a first time frame of a corresponding sequence of second communication-scheme time frames.
A more complete appreciation of the present invention and the scope thereof can be obtained from the accompanying drawings which are briefly summarized below, the following detailed description of the presently-preferred embodiments of the invention, and the appended claims.